The present invention relates, in general, to vehicle windshield wipers and, more specifically to windshield wiper park switches.
In vehicle windshield wiper drive apparatus, the wipers are provided with an automatic home or park position stop device which enables the wiper blades to return to the park position regardless of when a user turns off a wiper switch during the wiping cycle.
In a typical wiper park switch, an electrically conductive plate is provided with an electrically conductive and electrically non-conductive portions or traces. An electrical contact(s) fixed or otherwise driven by the drive gear coupled to the wiper drive motor cooperates with the electrically conductive plate to form a switch which opens and closes an electrical circuit to the power terminals of the wiper drive motor so that even when the user turns off the wiper switch during the wiping cycle, the electrically conductive plate and the contact(s) complete a circuit which enables the wiper motor to continue to operate to return the wiper blade to the park position. The contact(s) is typically driven or moved by the drive gear between the two positions, one forming a closed switch with the electrically conductive plate and the other forming an open circuit.
However, prior vehicle windshield wiper drive mechanisms of this type experience several problems. First, the park switch contact(s) is moved into and out of contact with the conductive traces on the conductive plate many times during a wiping operation. This causes wear of the contact and require a more robust wiper and contact design with adds to the cost of manufacturing the vehicle wiper. Despite such robust designs, the contacts are still susceptible to wear over long term use which could cause intermittent or loss of entire contact with the conductive plate.
Further, the contacts are susceptible to grease and other foreign materials which may be deposited on the conductive plate or the contacts which could also lead to loss of electrical contact with the conductive plate.
More importantly, prior wiper driving apparatus with conventional park switches frequently experience chatter when snow or other obstructions over a lower portion of the vehicle windshield prevent the wiper blades from returning to the park position. In this situation, the drive gear of the wiper motor is subjected to a force which acts in a direction counter to the normal direction of rotation of the drive gear. The snow or other obstruction places a spring force on the wiper blades which reverse drive the wiper blades and the attached drive gear away from the park position. Thus, as soon as the wiper drive motor is switched off by the park position switch, the reverse movement of the wiper blades and drive gear causes the contact(s) to re-engage the conductive portion of the conductive plate thereby reapplying electrical power to the wiper drive motor and causing the drive motor to restart movement of the wiper blades toward the park position. The blades are then placed in oscillation between park and non-park states which could lead to, damage to the wiper blades or wiper drive linkage, electrical wear of the electrical contacts and/or the wiper drive motor, as well as creating objectionable noise or chatter for the occupants of the vehicle.
Thus, it would be desirable to provide a windshield wiper drive apparatus which overcomes the above-mentioned problems encountered over the previously devised wiper park switches. It would also be desirable to provide a park switch mechanism for a vehicle windshield wiper drive apparatus which eliminates movable contacting portions for the park switch. It would also be desirable to provide a windshield wiper drive apparatus which has a single housing and drive gear design for different windshield wiper applications, including both intermittent and non-intermittent wiper apparatus.
The present invention is an improved windshield wiper drive apparatus which features a non-electrical contact position detection or sensor for detecting the inwipe or park position of the wiper blades. In another aspect, a portion of the non-electrical contact sensor is carried on a rotatable cam mounted in the windshield wiper drive housing which is rotated by the drive gear through interengaging members on the drive gear and the cam in the normal direction of rotation of the drive gear. Back drive of the drive gear does not result in reverse rotation of the cam thereby preventing chatter of the wiper blades.
In a specific aspect of the present invention, the windshield wiper apparatus includes a rotatable drive gear adapted to be coupled to a windshield wiper for driving the windshield wipers, a housing with the drive gear rotatably mounted in the housing, and a non-contact position sensor cooperatively arranged between the drive gear and the housing for detecting a rotation position of the drive gear corresponding to the windshield wiper park position.
Specifically, the position detector is formed of a magnetically responsive sensor mounted in the housing, a magnet movably disposed in the housing in an intersecting path of movement with respect to the sensor. The magnet is movable with the drive gear, with the sensor detecting each passage of the magnet therepast.
The magnet is mounted on the drive gear in one aspect of the present invention. In an alternate aspect, a cam is rotatably mounted in the housing. In this aspect, the magnet is mounted on the cam. Interengaging members on the drive gear and the cam cause rotation of the cam in the normal direction of rotation of the drive gear. The interengaging members are, in one example, projections formed on the cam and the drive gear which lie in intersecting rotatable paths.
The cam is arranged for only unidirectional rotation in the normal direction of rotation of the drive gear. Any back drive of the drive gear caused by the wiper blades hitting an obstruction when moving toward the park position separates the interengaging member on the drive gear from the cam leaving the cam in the park position and preventing the re-application of electrical power to the wiper drive motor.
The windshield wiper drive apparatus of the present invention overcomes several problems encountered with previous wiper apparatus, particularly contact wear and the oscillatory chatter and movement of the wipers when an obstruction prevents the wiper blades from reaching the full inwipe or park position.
The non-contact magnetic sensor employed in the present invention eliminates the direct electrical contact in previous wiper designs thereby increasing the long term reliable use of the wiper drive apparatus of the present invention. In the aspect of the invention where the magnet of the inventive position detector is mounted on the cam rotatably carried in the wiper drive housing, the cam is arranged for only unidirectional rotation thereby eliminating any re-application of electrical power to the wiper drive motor even if the wiper drive gear is back driven when the wiper blades hit an obstruction when moving toward the fall inwipe or park position.